As illustrated in FIG. 1, a temperature measuring device traditionally includes a temperature sensor 2 extended by an extension cable 3 making it possible to connect the temperature sensor to a measuring apparatus. The temperature sensor 2 traditionally includes a metal protective sheath 5 and a stop 6, mounted on the protective sheath 5 and adapted based on the targeted application.
The measuring apparatus 4 is intended to interpret the electrical signal supplied by the temperature sensor 2 and sent via the extension cable 3. This interpretation is an evaluation of the temperature to which the end of the temperature sensor is subjected.
Inside the protective sheath 5, the temperature sensor 2 traditionally includes a thermocouple 7 and a mineral insulator 8, traditionally made from alumina or magnesia, which allows the thermocouple to withstand environmental stresses, and in particular high temperatures.
As illustrated in FIG. 2, the thermocouple 7 is an assembly of first and second conductive wires 10 and 12, respectively, connected to one another and end to end at a hotspot 13. The difference in potential ΔU across the terminals of the first and second conductive wires depends on the difference between the temperature at the hotspot T1 and the temperature T0 across said terminals, according to the well-known Seebeck effect.
A temperature sensor with a thermocouple is in particular used in a heat engine unit, in which it is subject to temperatures comprised between −40° C. and 1200° C.
To manufacture a temperature sensor intended for such applications, the following steps are traditionally carried out:
First, a mineral insulated cable (MIC) 14 is manufactured.
A mineral insulated cable includes a metal protective sheath 5 and, inside the protective sheath 5, two thermocouple wires 10 and 12 made from a material suitable for forming a thermocouple, the two thermocouple wires being isolated from one another and from the protective sheath 5 using the mineral insulator 8 (FIG. 3a).
To form the junction between two thermocouple wires, or “hotspot” 13, a small amount of mineral insulator is removed from the ends of the cable, for example by sanding or scraping, typically over a depth of about 2 to 10 mm. At this so-called “distal” end, the two thermocouple wires thus emerge from the insulator, while being surrounded by the protective sheath 5 (FIG. 3b).
The two ends of the thermocouple wires thus freed are brought mechanically closer until coming into contact with one another, then are connected, for example by electric welding (FIG. 3c).
The hollowed end of the protective sheath can next optionally be filled with insulating material, identical to or different from the insulating material of the mineral insulated cable. The protective sheath is next closed (arrows of FIG. 3c) so as to protect the thermocouple, for example by electric welding (FIG. 3d).
Furthermore, after closing the protective sheath 5 or before cutting the mineral insulated cable, a throat 15 is traditionally produced at the distal end of the protective sheath 5, traditionally by wire drawing or hammering. The throat traditionally makes it possible to improve the response time of the temperature sensor without substantially affecting its ability to withstand vibrations.
Such a manufacturing method is difficult to automate and currently involves delicate manual operations.
There is therefore a need for a solution making it possible to facilitate the automation of the manufacture of a temperature sensor with thermocouple.
One aim of the invention is to meet this need.